Pseudoplastic water based ink for ballpoint pen

ABSTRACT

Provided is a water based ink for a writing instrument comprising at least a colorant, a dispersant, water and a polar solvent, wherein the ink contains 0.5 to 20% by weight of dextrin or maltodextrin based on the weight of the whole ink. It has an excellent drying resistance.

TECHNICAL FIELD

The present invention relates to a novel water based ink for a writinginstrument, more specifically to a water based ink for a writinginstrument having an excellent drying resistance including apseudoplastic water based ink for a ballpoint pen.

BACKGROUND ART

Inks for a ballpoint pen include usually a low-viscosity water based inkfor a ballpoint pen which contains a solvent comprising a water basedsolvent such as water and has an ink viscosity of 10 mPa.s or less andan oil based ink which contains a solvent comprising an oil basedsolvent such as a mineral oil, a polyhydric alcohol, a fatty acid andCellosolve and has an ink viscosity of 1000 to 20000 mPa.s.

A ballpoint pen using an oil based ink for a ballpoint pen has suchstructure that the ink adhered on a ball at a pen tip through an inkreservoir having a small diameter is transferred onto a paper surface byrotation of the ball and only the transferred portion of the ink is fedto the ball from the reservoir.

A ballpoint pen using a water based ink for a ballpoint pen has suchstructure that the ink is fed to a ball surface and a paper surface byvirtue of capillary action of a feed prepared by binding fine fibers.

While the foregoing water based ink for a ballpoint pen and the oilbased ink for a ballpoint pen each have excellent advantages, they alsohave various problems, respectively. For example, since the water basedink for a ballpoint pen has a low viscosity, the ink is fed by means ofmaking use of a principle of capillary action, and a ballpoint pen usingthis allows the capillary action to work on the contact point thereof tofeed the ink only if the point portion of the ballpoint pen is simplybrought into contact with paper and makes it possible to write finelines on a paper surface without applying so higher writing pressure, sothat splitting, starving and blobbing scarcely take place. On thecontrary, storing the ink directly in the ink reservoir allows the inkto seep due to vibrations, impacts and a rise in a open air temperatureto make the amount of the ink to be fed to the ball unstable.Accordingly, complicated structure having a feed prepared by bindingfine fibers is required. Further, involved is the problem that it isdifficult to check the remaining amount of the ink.

On the other hand, a ballpoint pen using an oil based ink for aballpoint pen is characterized by that because of a high viscosity ofthe ink, blobbing of the ink from the pen point can be prevented and theink can be stored directly in the ink reservoir having a small diameter,so that the structure of the ballpoint pen can be simplified and thatthe remaining amount of the ink can be checked by using a transparentmaterial for the ink reservoir. On the other hand, there are involvedthe problems that since the ink is transferred only on a paper surfacecontacted with the rotating ball, splitting and starving are liable tobe caused if the ball rotates unstably and that since the ink hardlypenetrates into the paper surface, blobbing which causes stain with theuntransferred ink is apt to be caused.

In recent years, in order to solve such problems, provided are waterbased inks for a ballpoint pen in which a gelatinizer or a water-solublepaste are added to impart a specific viscosity characteristic(hereinafter referred to as a pseudoplastic water based ink).

A ballpoint pen using this pseudoplastic water based ink is reduced inan ink viscosity because shear force is applied to the ink due to therotation of the ball at the tip point at the time of writing, and canwrite as smoothly as a ballpoint pens using a water based ink and makefine lines on the paper surface. Further, blobbing of the ink from thepen point can be prevented because the ink has a high viscosity when thepen is not used for writing. The ballpoint pen using this pseudoplasticwater based ink can store the ink directly into the ink reservoir andsimplify the structure thereof, and the use of a transparent materialfor the ink reservoir makes it possible to check the remaining amount ofthe ink.

Thus, the use of the pseudoplastic water based ink for a ballpoint penprovides a writing instrument having both characteristics of a ballpointpen using a water based ink and a ballpoint pen using an oil based ink.

A water based ink contains water as a principal solvent and thereforehas the defect that if water contained therein evaporated, dissolvedsubstances and mixtures contained in the ink are concentrated,deposited, dried and solidified at the point of the writing instrumentto cause clogging and a rise in the viscosity of the ink and bring abouttroubles in writing. Accordingly, it has so far been proposed to add aless volatile agent for solubilizing a dye or a less volatile aid fordissolving a dye such as urea, thiourea, polyhydric alcohols orderivatives thereof, tetrahydrofurfuryl alcohol,4-methoxy-4-methylpentane-2-one and ethylene oxide adducts ofp-toluenesulfonamide and thiodiethanol, alkanolamine, and sorbitol.

However, inks blended with the various additives described above havenot been satisfactory for writing instruments because of the reasonsthat the drying resistant effect is insufficient and the additivesthemselves have toxicity and therefore are not suitable as additives andthat the viscosities of the inks grow large to bring about inferiorfollow-up of the inks.

Thus, an object of the present invention is to provide a water based inkfor a writing instrument which has an excellent drying resistance and issafe and in which the viscosity does not rise. In particular, a waterbased ink which is suitable as a pseudoplastic water based ink for aballpoint pen is provided.

DISCLOSURE OF THE INVENTION

The present invention provides a water based ink for a writinginstrument comprising at least a colorant, a dispersant, water and apolar solvent, wherein the ink contains 0.5 to 20% by weight of dextrinor maltodextrin based on the weight of the whole ink. In particular, apseudoplastic water based ink for a ballpoint pen comprising aviscosity-controlling agent as well as at least a colorant, adispersant, water, a polar solvent is one preferred embodiment of thepresent invention.

Other prescribed water soluble organic solvents may be added to thewater based ink for a writing instrument of the present invention aloneor in combination of a plurality thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

The components used in the water based ink for a writing instrument ofthe present invention shall be described.

Dextrin and maltodextrin added to the water based ink for a writinginstrument in the present invention are non-toxic and safe saccharideswhich are usually used as an edible sweetening and is characterized bythat they have a high solubility in water and have a very excellentwater retentivity.

Accordingly, a water based ink for a writing instrument containing thisdextrin or maltodextrin is safe and makes it possible to elevate dryingresistance without bringing about a problem that the ink viscosity isincreased with the lapse of time.

Since dextrin or maltodextrin does not exert an adverse influence on theproperties of water based inks usually used and does not change ahydrogen ion concentration in the ink, it does not exert an adverseinfluence on anionic and cationic substances and therefore has theadvantage that a colorant can optionally be selected from all of waterbased dyes and organic or inorganic pigments.

The content of dextrin or maltodextrin in the water based ink of thepresent invention is preferably 0.5 to 20% by weight based on the weightof the whole ink. If the content is smaller than 0.5% by weight, theeffect on the drying resistance is reduced, and if it is larger than 20%by weight, the spinnability becomes stronger, so that the writingfeeling is deteriorated.

All dyes and pigments which can be dissolved or dispersed in water basedsolvents can be used as the colorant. To give specific examples thereof,there can be used, acid dyes such as Eosine, Floxine, Water Yellow #6-C,acid red, Water Blue #105, Brilliant Blue FCF and Nigrosine NB, directdyes such as Direct Black 154, Direct Sky Blue 5B and Violet BB, basicdyes such as Rhodamine and Methyl Violet, inorganic pigments such astitanium dioxide, carbon black and ultramarine, organic pigments such asCopper Phthalocyanine Blue and Benzidine Yellow, and various metalpowders. They can be used alone or in a mixture of two or more kindsthereof.

When a pigment is used as the colorant, a water-soluble polymerdispersant and a surfactant have to be suitably selected and blended.The water-soluble polymer includes anionic polymers such as polyacrylicacid salts, salts of a styrene-acrylic acid copolymer, salts of astyrene-maleic acid copolymer, salts of a vinylnaphthalene-maleic acidcopolymer and a β-naphthalenesulfonic acid-formalin condensationproduct, and nonionic polymers such as polyvinyl alcohol,polyvinylpyrrolodone and polyethylene glycol.

Water can be used as the principal solvent, and all solvents havingpolar groups which are missible with water can be used as the polarsolvent. There can be used, for example, ethylene glycol, diethyleneglycol, triethylene glycol, polyethylene glycol, propylene glycol,ethylene glycol monomethyl ether, glycerin, pyrrolidone andtriethanolamine.

The viscosity-controlling agent is used for providing the ink with apseudoplasticity, and to be specific, there can be used polyacrylic acidsalts, cross-linking type acrylic acid polymers, salts of astyrene-acrylic acid copolymer, salts of a styrene-maleic acidcopolymer, nonionic polymers such as polyvinylpyrrolodone andpolyethylene glycol, and polysaccharides such as xanthane gum, guar gum,casein, gum arabic, gelatin, carrageenan, alginic acid, tragacanth gum,and locust bean gum.

Further, the ink which is controlled by these viscosity-controllingagents has a viscosity falling preferably in a range of 100 to 4000mPa.s when the shearing rate is 3.84 s⁻¹. If the viscosity is lower than100 mPa.s under the condition described above, the ink is blobbed fromthe pen tip. Further, when a colorant having a large specific gravitysuch as titanium dioxide and metal powder is used, the viscosity has tobe controlled rather high in order to prevent the colorant fromsettling, and the upper limit thereof is preferably 4000 mPa.s. If theupper limit exceeds 4000 mPa.s, there is a risk to bring about areduction in the writing property due to inferior follow-up of the ink.

Other controlling agents than the components described above which canbe used if necessary include a lubricant such as polyalkylene glycolderivatives, fatty acid alkali salts, nonionic surfactants and fluorinebase surfactants, a rust preventive such as benzotriazole and saponins,a pH controlling agent such as potassium hydroxide and potassiumphosphate, and a preservative such as sodium omadine and1,2-benzoisothiazoline.

The water based ink for a writing instrument of the present inventioncan easily be obtained by a production method in which the componentsdescribed above are dissolved, if necessary, with heating and mixedunder stirring.

EXAMPLES

The present invention shall more specifically be explained below withreference to examples, but the present invention shall by no means berestricted by these examples.

Example 1

A blue, water based pigment ink for a ballpoint pen was preparedaccording to the following recipe:

Phthalocyanine blue 8.0% by weight Styrene-acrylic acid resin 3.0% byweight ammonium salt Ethylene glycol 20.0% by weight Dextrin 5.0% byweight Phosphoric acid ester 0.7% by weight Bioden 0.3% by weightAminomethylpropanol 0.3% by weight Benzotriazole 0.2% by weightIon-exchanged water balance

Example 2

A blue, water based pigment ink for a ballpoint pen was preparedaccording to the following recipe:

Phthalocyanine blue 8.0% by weight Styrene-acrylic acid resin 3.0% byweight ammonium salt Ethylene glycol 20.0% by weight Maltodextrin 4.0%by weight Phosphoric acid ester 0.5% by weight Bioden 0.3% by weightAminomethylpropanol 0.3% by weight Benzotriazole 0.2% by weightIon-exchanged water balance

Example 3

A black, water based ink for a felt-tip pen was prepared according tothe following recipe:

Carbon black 8.0% by weight Styrene-acrylic acid resin 3.0% by weightammonium salt Maltodextrin 3.0% by weight Ethylene glycol 20.0% byweight Bioden 0.3% by weight Aminomethylpropanol 0.3% by weightBenzotriazole 0.2% by weight Ion-exchanged water balance

Comparative Example 1

Dextrin was removed from the ink of Example 1 to prepare a blue, waterbased ink for a ballpoint pen.

Comparative Example 2

Maltodextrin was removed from the ink of Example 2 and 5% by weight ofurea was added to prepare a blue, water based ink for a ballpoint pen.

Comparative Example 3

Maltodextrin was removed from the ink of Example 3 to prepare a black,water based ink for a felt-tip pen.

The inks obtained according to the foregoing recipes of Examples 1 to 2and the inks obtained according to the recipes of Comparative Examples 1to 2 were charged respectively into ballpoint pens having a balldiameter of 0.7 mm, and the inks obtained according to the recipes ofExample 3 and Comparative Example 3 were charged respectively intocommercially available felt-tip pens. They were left standing with thecaps unfastened, and the time passed until starving was caused wasdetermined. Further, a change in the viscosity of the inks was observedafter stored at 50° C. for one month. The results thereof are shown inTable 1.

TABLE 1 performance evaluation of the inks Example Comparative Example 12 3 1 2 3 Time 30 30 16 15 20 5 until days days hours days days hoursstarving Viscosity None None None None Rise None change

Example 4

A blue, pseudoplastic water based pigment ink for a ballpoint pen wasprepared according to the following recipe:

Phthalocyanine blue 8.0% by weight Styrene-acrylic acid resin 3.0% byweight ammonium salt Ethylene glycol 20.0% by weight Dextrin 5.0% byweight Phosphoric acid ester 0.7% by weight Bioden 0.3% by weightAminomethylpropanol 0.3% by weight Benzotriazole 0.2% by weightPolyacrylic acid salt 0.4% by weight (acryl base synthetic polymer)Ion-exchanged water balance

Example 5

A blue, pseudoplastic water based pigment ink for a ballpoint pen wasprepared according to the following recipe:

Phthalocyanine blue 8.0% by weight Styrene-acrylic acid resin 3.0% byweight ammonium salt Ethylene glycol 20.0% by weight Maltodextrin 4.0%by weight Phosphoric acid ester 0.5% by weight Bioden 0.3% by weightAminomethylpropanol 0.3% by weight Benzotriazole 0.2% by weightPolyacrylic acid salt 0.4% by weight (acryl base synthetic polymer)Ion-exchanged water balance

Example 6

A black, pseudoplastic water based pigment ink for a ballpoint pen wasprepared according to the following recipe:

Carbon black 8.0% by weight Styrene-acrylic acid resin 3.0% by weightammonium salt Maltodextrin 3.0% by weight Potash soap 0.5% by weightPropylene glycol 20.0% by weight Bioden 0.3% by weightAminomethylpropanol 0.3% by weight Benzotriazole 0.2% by weightCross-linking type acrylic 0.4% by weight acid polymer Ion-exchangedwater balance

Comparative Example 4

Dextrin was removed from the ink of Example 4 to prepare a blue, waterbased ink for a ballpoint pen.

Comparative Example 5

Maltodextrin was removed from the ink of Example 5 and 5% by weight ofurea was added to prepare a blue, water based ink for a ballpoint pen.

Comparative Example 6

Maltodextrin was removed from the ink of Example 6 to prepare a black,water based ink for a ballpoint pen.

The inks obtained according to the foregoing recipes of Examples 4 to 6and the inks obtained according to the recipes of Comparative Examples 4to 6 were charged respectively into ballpoint pens having a balldiameter of 1.0 mm. They were left standing with the caps unfastened,and the time passed until starving was caused was determined. Further,the viscosity of the initial inks at a shearing rate of 3.84 s⁻¹ and achange in the viscosity of the inks after stored at 50° C. for one monthwere observed. The results thereof are shown in Table 2.

TABLE 2 performance evaluation of the inks Example Comparative Example 45 6 4 5 6 Time 10 14 14 3 5 5 until days days days days days daysstarving Initial 700 500 500 750 800 550 Viscosity of ink (mPa · s)Viscosity None None None None Rise None change

INDUSTRIAL APPLICABILITY

The water based ink of the present invention for a writing instrument isvery safe and does not bring about the trouble that the viscosity riseswith the passage of time. It has a very excellent drought resistance andis suitable to felt-tip pens and ballpoint pens, and particularly thepseudoplastic water based ink is suited to ballpoint pens using a waterbased ink.

What is claimed is:
 1. A pseudoplastic water based ink for a ball pointpen comprising at least a colorant, a dispersant, water, a polar solventand a viscosity-controlling agent, wherein said ink contains 0.5 to 20%by weight of dextrin or maltodextrin based on the weight of the wholeink, wherein said ink has a viscosity of 100 to 4,000 mPa's at ashearing rate of 3.84 s⁻¹.
 2. The pseudoplastic water based ink for aballpoint pen as described in claim 1, wherein the viscosity-controllingagent is at least one selected from polyacrylic acid salts,cross-linking type acrylic acid polymers, salts of a styrene-acrylicacid copolymer, salts of a styrene-maleic acid copolymer,polyvinylpyrrolidone, polyethylene glycol, xanthan gum, guar gum,casein, gum arabic, gelatin, carrageenan, alginic acid, tragacanth gum,and locust bean gum.